Key Specifications. Waveguide Size 1 WR-28 Waveguide Size 2 WR-28 Frequency, Min 30 GHz Frequency, Max 40 GHz Lowband Min Rejection 50. Highpass Waveguide Filter With WR-28 Interface Operating from 30 GHz to 40 GHz. The PE-W28F012 is a WR-28 highpass filter with UG Cover Flanges. The pass band is 10 GHz, or 30 to 40 GHz. Implementing a waveguide design, the filter has excellent rejection of 50 dB minimum at 22 GHz, or about 8000 MHz from the band edge. It has a maximum insertion loss of 0.5 dB.